Videotex, teletext and general information retrieval systems are a rapidly emerging technology in which a user located at a home or office station, using hardware such as a dedicated terminal, communicates over an appropriate channel, such as the telephone system, with a host computer having access to a stored data bank or other service facilities. Appropriate software causes the host computer to interact with the user so that requests for information are translated into search routines which scan the data bank to locate the desired material. Some such systems are also capable of providing other services, such electronic banking, shopping, and the like.
One of the problems which information retrieval systems present is the sheer difficulty of finding relevant information amongst the large amount of material which must be included in the data bank in order to make the system useful and economical. One way to aid the search for such needles in the electronic haystack is to store as sequentially numbered pages a linked sequence of information blocks which are all related to a common subject. Where the subject is one which lends itself to a number of classifications and subclassifications, the link sequence is typically a vertically branching data structure which stems from a common trunk and repeatedly divides and subdivides. Once the beginning of the chain is located in some manner, this system permits the user to step successively through these related pages, exploring each branch until the desired information is located.
But sometimes the user wishes to browse through the system in a different order. For example, after having located the general area of the database which contains the desired broad subject category, the user may need to search within that general area to determine which particular subdivision thereof is most likely to contain the specific information sought. Stepping through the general area in page order would probably be an inefficient search strategy under those circumstances, because the user would typically have to traverse each of several nonrelevant branches of the tree structure down to a low level of specificity before finding the one branch which is most relevant.
What is needed, therefore, is a means for browsing "horizontally," i.e. moving across the tree structure, until the most relevant branch is located, after which the user can then revert to the conventional strategy of descending "vertically" along that particular branch to the desired level of specificity.